1) Tanking Up
Most singers inhale as deeply and as fully as they possibly can as they prepare to sing each line of their songs or their vocal exercises, often in an attempt to avoid running out of air before the end of their vocal tasks. They may have also been taught that more air necessarily means a better supported tone. However, ‘tanking up’ or ‘overcrowding the lungs’ like this unnecessarily increases the subglottic pressure (the air pressure below the larynx). For shorter exercises and phrases, less air is needed to fuel the voice. If appoggio technique (the ‘inspiratory hold’) is maintained, the outgoing air will be slowly and steadily paced, and there will be no need to fill up on air for shorter vocal tasks. It is critical that the singer learn to gauge precisely how much air is appropriate for the upcoming vocal task, and then inhale only the necessary amount of air. There should not be a tremendous amount of air ‘left over’ at the end of the phrase.
Singers who tank up also often have a tendency to close off the glottis in order to stop the tone, employing the adductor muscles (those which close the glottis) instead of the abductor muscles (those which open the glottis) to stop phonation. Sometimes, the singer does so in a attempt to ensure precision of the release of the note. Oftentimes, however, this habit leads to a lowering of pitch at the end of the note, as well as a noisy release of the remaining and excess air after the note has ended because the closure of the glottis at the end of the phrase in combination with excessive amounts of air remaining in the lungs causes an increase in subglottic pressure, pressing of the vocal folds together and a ‘pressurized’ release. Learning to draw in less air to begin with, to pace the outgoing breath slowly and steadily and to release the note precisely but with a relaxed and open throat will solve this problem.
2) Pushing Out the Air
Ideally, we want to think of the air as being ‘allowed’ out, rather than being ‘pushed’ out, to create voice. I use a balloon analogy – and have actually used this as an exercise with real balloons in group voice classes – that helps to illustrate this concept. When we inflate a latex balloon (lungs) and pinch the mouth of the balloon (closing the glottis, or approximating the vocal folds), air pressure immediately begins to build up. When we stretch the mouth of the balloon, allowing air to slowly seep out, the latex begins to rapidly chop the exiting air into tiny puffs, thus creating sound (voice). If the mouth of the balloon is stretched tighter and pulled longer (as what happens when the larynx pivots to elongate and tighten the vocal folds), higher pitch is created. Now, suppose for a minute that we decide to ‘help’ the air make its exit by squeezing the body of the balloon (as when we compress the air with a diaphragm that has been forced upward by abdominal muscles). What we will hear is a louder initial sound, yes, but also a less pleasant and more unsteady tone. Additionally, the air will be lost more rapidly.
In the case of the human voice, pushing in with and contracting the abdominal wall will tend to lead to either pressed phonation (a ‘shouty’ or forced voice quality) or a breathy quality after the initial onset due to the vocal folds being blown apart by the forceful air. Singers must be assured that the air will flow out of their lungs virtually on its own, thanks to the elastic recoil of the lungs, and there is, therefore, no need to either ‘help’ it along or to force it out. (This is why we should learn to relax the abdominal muscles.) Of course, different styles and techniques may require a more forceful expulsion of air in order to create the desired sound, but as a general rule, too much air being forced out of the lungs is both unnecessary and unhealthy.
3) Holding Back the Air
Many singers hold back the air, or choke it off, either at the laryngeal level, in which the singer closes the glottis immediately after inhalation and briefly pauses before producing voice (known as compression of the breath), or at the supraglottic level, in which the muscles of the throat constrict or squeeze and inhibit the airflow. Holding back the air in these manners are the result of poor coordination between the breathing mechanism and the larynx. In both cases, subglottic pressure will rise, forcing the glottis to have to work harder, and opening up the door to potential injury. The voice will also sound less steady and free. The singer who briefly holds in the air before singing needs to develop the coordination of inhaling then immediately turning that breath into tone. For the singer who tends to cut off or hold back the breath with the muscles of the vocal tract, training in the Farinelli exercise, which I describe below, will help him learn to maintain more openness and relaxation of the vocal tract. Singing with a more open and relaxed throat is critical.
Singers who choke off the breath, especially at the release of the note, can practice briefly sustaining a vowel on a comfortable pitch, then gradually allowing that tone to become just a stream of air (with no vocal sound). Gradually increasing the space in the glottis (moving from closed glottis to partially open glottis to open glottis) may require some practice, as it will be a new and challenging coordination to learn. For most singers who first try this exercise, they find that they have difficulties maintaining the same pitch (and some can’t sustain voice) once the glottis starts to open. The key is making this change from a ‘clean’ tone to a breathy tone to no voice (only exiting air) gradual and controlled. Higher pitches can be tried once the singer can successfully execute this exercise within speech-inflection range.
source: http://www.singwise.com/cgi-bin/main.pl?section=quickRef&doc=Breathing_InAPinch